This invention relates to method and apparatus for generation of plural pulse beams of charged particles, including electrons and other charged particles of heavier mass, and more specifically to such method and apparatus applicable to intense relativistic high energy electron beams.
In the art of acceleration of charged particles and the like, it is known to utilize apparatus incorporating electromagnetic fields for acceleration of such particles. Similarly it is known to utilize apparatus having resonant cavities disposed along a longitudinal trajectory of such charged particles in order to modify the energy distribution of the particles and thus to modify the characteristics of the beam produced thereby.
For example, the use of charged transmission lines as applied to high-current electron accelerators is described in Eccleshall et al., 49 Journal of Applied Physics, 7, July 1978, pp. 3649-3655, as well as in M. Friedman, 31 Physical Review Letters, 18, Oct. 29, 1973, pp. 1107-1110.
In the latter, a foilless diode is utilized in a structure incorporating an electromagnetic coil surrounding a drift chamber and forming therewith an autoaccelerator producing intense relativistic electron beams. An annular electron beam having a current of approximately 10 kiloamperes and a voltage of approximately 500 kilovolts is produced for a duration of approximately 50 nanoseconds. The magnetic field produced by an electromagnetic coil is used to confine spread of the produced electron beam. In the Eccleshall paper there is illustrated the use of resonant cavities, contacting the path of the electron beam, to modify characteristics of the beam current.
Yet a further illustration of the prior art is provided in Friedman U.S. Pat. Nos. 4,038,602 and 4,215,291, and in Miller U.S. Pat. No. 4,070,595, relating to structures for particle acceleration.
None of the prior art references, however, relate to the production of a separate electron beam pulse in response to a primary, or incident, beam pulse. In the prior art disclosures, an externally generated electron current beam pulse is modified with respect to energy distribution and the like, utilizing structure such as resonant cavities, for example. However, various characteristics of the incident beam must remain fixed, and no provision is made for the generation and production of a second, time distinct, intense relativistic electron beam. Such production in the prior art may thus only be achieved by the repeated use of the beam generating structure or by a complex alignment of a plurality of such structures, each producing a separate beam. It is thus difficult to obtain a sequence of high energy high current pulses of charged particles for use in radiographic imaging of rapidly changing objects, for example.
There is thus a need in the prior art to provide a simplified structure for generating sequential intense beams of charged particles, each traversing substantially the same path and separated in time from one another.